The present invention relates in general to alkaline storage batteries and more particularly to nickel-hydrogen storage batteries and it utilizes the high energy and power densities of the nickel-hydrogen electrochemical pair in a practical construction affording improved protection against the failure modes of burnout, drying and explosion to provide reliable, long life operation of such cells consistent with high performance.
Nickel-hydrogen secondary batteries known to the art comprise multi-cell arrays within a pressure vessel. Each cell has a positive (during discharge), nickel-containing electrode, consistently designated as, "cathode" herein, spaced from a hydrogen-containing negative (during discharge) electrode consistently designated as "anode" herein. The electrodes generally have the form of spaced plates separated by a porous inert sheet, such as polypropylene or nylon, which acts as a separator matrix for electrolyte extending between the two electrodes. The separator matrix sheet is sufficiently thick to prevent short circuit contact between the electrodes and holds a sufficient quantity of electrolyte for desired cell performance. The electrolyte is an alkaline medium, preferably an aqueous solution of alkali metal hydroxide, more particularly thirty percent potassium hydroxide solution. The hydrogen-containing electrode is a plastic bonded, metal powder plate. The metal is preferably platinum, but may comprise other materials which will catalyze hydrogen oxidation reactions in aqueous electrolyte media and is backed by a plastic, preferably tetrafluoroethylene (e.g., Dupont's Teflon brand materials), mesh element which accommodates gas diffusion. The cathode material is a nickel-oxy-hydroxide. Pairs of such cells are generally arrayed with their cathodes back to back. External contact to the electrodes is generally made by nickel
Hydrogen within the pressure vessel, generally maintained at superatmospheric pressure of 20-50 atmospheres, diffuses through the gas diffusion mesh of Teflon or the like to reach the catalytic anode where the discharge mode anode reaction,
(I) 1/2 H.sub.2 + OH.sup.- .fwdarw. H.sub.2 O + e.sup.- occurs, in balance with the corresponding cathode reaction, PA1 (II) NiOOH + H.sub.2 O + e.sup.- .fwdarw. Ni(OH).sub.2 + OH.sup.- providing an overall discharge reaction, PA1 (III) NiOOH + 1/2 H.sub.2 .fwdarw. Ni(OH).sub.2
The reverse of such reactions occur on charging. The charge and discharge conditions, cell constructions and operating data are more particularly described in the published article by Giner and Dunlop, "The Sealed Nickel-Hydrogen Secondary Cell" Journal of the Electrochemical Society, Volume 122, number 1, pages 1-11 (January 1975), incorporated herein by reference. The system is an attractive one to workers in the field because of several favorable properties including improved energy density and power density compared to many other electrochemical couples, including nickel-cadmium.
It is an important object of the invention to improve the resistance of nickel-hydrogen batteries to one or more of the failure modes of burnout, drying and explosion.
It is a further object of the invention to maintain high performance of such batteries in terms of energy and power density consistent with the preceding object.
It is a further object of the invention to make only minimal changes in weight and volumetric envelope considerations applicable to such batteries consistent with one or more of the preceding objects.
It is a further object of the invention to stabilize the conditions of cyclic charge and discharge consistent with one or more of the preceding objects.